The present invention relates to an inertia impactor for classifying and collecting aerosols in the fields of environmental pollution particle measurement and control, and more particularly to an impactor with a cooled impaction plate capable of efficiently separating aerosols by cooling the impaction plate below a temperature of fluid inflowing into the impactor, and to a method classifying and collecting the aerosols by using the same.
Recently, as the environmental pollution becomes an important issue, it is more and more necessary to study and develop an environmental pollution measurement apparatus and an equipment for environment pollution materials research. Of the devices, an impactor is frequently used to measure and control aerosols which are one of the main components causing the atmospheric pollution. Namely, the impactor separates, collects and measures aerosols by using inertia of the aerosol whose size is less than 10 xcexcm, since it has been developed by the environmental particle researchers in 1970s.
The impactor separates the aerosols flowing along a predetermined path into ones having relatively small inertia and the others having relatively large inertia by suddenly changing the flowing path. Namely, when the flowing path is changed, the aerosols which have small inertia are continuously flowing along the path, however the aerosols which have large inertia are getting out of the flowing path due to their own large inertia. Therefore, the impactor can collects the aerosols which are out of the flowing path.
FIG. 1 shows a cross-sectional view of the conventional impactor which includes an accelerating nozzle 20 with a hole accelerating the movement of the aerosols, thereby enlarging their inertia, and an impaction plate 30 for collecting some aerosols which have relatively large inertia.
When fluid including aerosols inflows toward the impactor by external pressure or internal suction, the fluid is accelerated at the accelerating nozzle 20. The aerosols having inertia larger than a critical value among the accelerated aerosols are adhered to the impaction plate 30, and the aerosols having inertia lower than the critical value are continuously flowing together with the fluid along the path.
In the conventional impactor, the inertia is measured by a Stoke""s number that is calculated from the kinetic equation of the aerosols. The Stoke""s number is defined as follows:
St (Stoke""s number)=xcfx81pCVD2/9xcexcW xe2x80x83xe2x80x83(1)
where xcfx81p represents a density of the aerosols, C denotes a slip correction factor of the aerosols, V denotes an average velocity of fluid passing through the accelerating nozzle 20, D is a diameter of the aerosols, xcexc is a viscosity of the fluids, W is a diameter or width of the accelerating nozzle 20.
The Stoke""s number defined as above represents the inertia magnitude of the aerosols in the impactor, and a classification performance is presented by the Stoke""s number.
In order to effectively classify or separate the aerosols according to the prior art, the impaction plate of the impactor is coated by some coating materials. However, the condition that these coating materials can not be used, happens in several cases.
For example, (1) when the aerosols generated in high temperature are sampled, the coating materials become unstable in high temperature, therefore the coating materials can not function properly because the coating materials have liquidity to fall down or vaporized, (2) when the bio-aerosols are sampled by using the impactor with coating materials, it is difficult to analyze the bio-aerosols precisely because the bio-aerosols are contaminated with coating materials.
At those situations in which the coating materials can not be used, the impactor classification efficiency dramatically decrease.
Consequently, because of the condition that the coating materials cannot be used in an impactor, a new impactor having higher classification efficiency without using coating materials is required.
It is an object of the present invention to provide an impactor with a cooled impaction plate which makes the classification efficiency high without using coating materials by using condensational phenomena and thermophoresis phenomena which represent the kinetic characteristics of the aerosols, and a method classifying and collecting the aerosols using the same.
In order to achieve the object of the present invention, the impactor with a cooled impaction plate is designed, which comprises: an accelerating nozzle for accelerating movement of the aerosols; an impaction plate for changing the flowing direction of the aerosols by means of impacting the aerosols exhausted from the accelerating nozzle, and for collecting the aerosols which are out of the flowing path of the aerosols and have larger inertia than critical value, wherein the impaction plate is installed apart from an outlet of the accelerating nozzle; and cooling means for cooling the impaction plate below a temperature of fluid inflowing into the impactor, wherein the cooling means is fixedly installed at the impaction plate.
In order to achieve the object, the method classifying and collecting aerosols in atmosphere by using an impactor with a cooled impaction plate, comprises the steps of: cooling an impaction plate below a temperature of fluid inflowing into the impactor; exhausting the aerosols from an accelerating nozzle into the impaction plate which is installed apart from an outlet of the accelerating nozzle; changing the flowing direction of the aerosols by means of impacting the aerosols exhausted from the accelerating nozzle; and collecting the aerosols which are out of the flowing path of the aerosols and have larger inertia than critical value.
Preferably, the cooling means is a thermoelectric device fixed at the impaction plate.
More preferably, the thermoelectric device is fixed at the opposite side of an aerosol impacting surface of the impaction plate 30.
Also, the cooling means maintains the temperature of the impaction plate 30 within 0xc2x0 c.xcx9cxe2x88x925xc2x0 c.
Preferably, a diameter of an inlet of the accelerating nozzle 20 is larger than a diameter of an outlet 21 of the accelerating nozzle 20.